<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    
        .box{
            width: 100px;
            height: 100px;
            background-color: gold;
            /*margin-left:auto;
            margin-right: auto;*/
            
            /*让盒子在父级里左右居中*/
            margin: 0 auto;
        }
    
    </style>
</head>
<body>
    

    <div class="box"></div>


</body>
</html>